In the present disclosure, the remote vehicle (the crossing vehicle) may include a vehicle that enters the intersection from an opposite lane of the host vehicle and turns left or right to move in the direction intersecting with the moving direction of the host vehicle.
Japanese Unexamined Patent Application Publication No. 2005-227978 discloses a collision avoidance system in which, in order to assist avoidance of a collision of a host vehicle with a remote vehicle, a control unit operates a warning unit if it is determined that the probability of collision of the host vehicle with the remote vehicle is high to alert a driver (paragraphs [0030] to [0032] of Japanese Unexamined Patent Application Publication No. 2005-227978).
The collision avoidance system disclosed in Japanese Unexamined Patent Application Publication No. 2005-227978 is mentioned in Japanese Unexamined Patent Application Publication No. 2010-282283. Specifically, Japanese Unexamined Patent Application Publication No. 2010-282283 indicates that a certain start-up distance from an intersection within which a host vehicle issues a warning is set to a fixed range (paragraph [0002] in Japanese Unexamined Patent Application Publication No. 2010-282283).
In addition, Japanese Unexamined Patent Application Publication No. 2010-282283 discloses a technology to increase the start-up distance as the degree of congestion of remote vehicles around the host vehicle at the intersection is increased and to decrease the start-up distance as the degree of congestion is decreased.
However, when the degree of congestion of remote vehicles around an intersection which a host vehicle is to enter is high, the sense of tension (attention) of a driver of the host vehicle to the front including the intersection is increased, compared with a case in which the degree of congestion of the remote vehicles is low. Accordingly, when the start-up distance from the intersection for the issuance of the warning is increased with the increasing degree of congestion of the remote vehicles, as in Japanese Unexamined Patent Application Publication No. 2010-282283, excessive warning may be issued to make the driver troublesome, thus leaving a room for improvement.
In contrast, when the degree of congestion of remote vehicles around an intersection which a host vehicle is to enter is low, the sense of tension (attention) of the driver of the host vehicle to the front including the intersection is decreased, compared with the case in which the degree of congestion of the remote vehicles is high. Accordingly, when the start-up distance from the intersection for the issuance of the warning is decreased with the decreasing degree of congestion of the remote vehicles, as in Japanese Unexamined Patent Application Publication No. 2010-282283, the timing of the warning may be delayed, thus also leaving a room for improvement.